Clooney's Obama fundraiser is expected to raise $15 million, mostly from general public donations for a chance to attend. It comes as fundraising changes.

President Barack Obama talks with actor George Clooney outside the Oval… (Pete Souza, The White House )

As political fundraisers go, it's set to be an "Avengers"-sized blockbuster: One hundred and fifty wealthy Democrats will dine with President Obama at George Clooney's Studio City home Thursday night, at a party that organizers expect to gross $15 million for the president's re-election campaign — the highest amount ever raised at such an event.

But the Hollywood VIPs paying $40,000 a ticket will account for just over one-third of Obama's haul Thursday night; the rest is coming from members of the general public lured by an online contest that has astutely leveraged Clooney and Obama's joint star power. Tens of thousands of Americans have contributed donations averaging $23 each for a chance to win a ticket to the soiree. Two winners and their guests will attend the party, where the president is expected to discuss policy in the low-key environment of Clooney's canyon home over a dinner catered by Wolfgang Puck.

Recognizing the dual appeal of Obama and Clooney, the campaign pitched the contest to potential contributors in emails with subjects like "Clooney and me," "A little fun" and "We'll take care of airfare." A random drawing narrowed the pool of finalists down to 50, and the campaign then planned to do background checks on those 50 before notifying the two winners, whose identities will be revealed Thursday.

"It's a stunning turnout of support, and what's really interesting to me is that almost two-thirds of the money is coming from grass-roots support, from the 99%," Katzenberg said. The full-ticket-price guests will come from a number of industries in Los Angeles, he said, including movies, TV, music, finance, law and healthcare.

Though the dinner will help fill Obama's coffers, it's not entirely without risk. The lucrative, starry affair is bringing attention to Obama's show business ties just as his campaign is fending off criticism that he's more pop culture hotshot than effective statesman. A recent ad from the pro-GOP super PAC American Crossroads mocked Obama as a "celebrity president," cutting together clips of him appearing on "Late Night With Jimmy Fallon" and singing Al Green's "Let's Stay Together" with dreary statistics on unemployment and student loan debt.

"This event will help Obama regain some of his cool," said GOP media strategist Fred Davis, whose 2008 ad for John McCain compared candidate Obama to Paris Hilton. "But they're missing the point if they think cool is gonna re-elect him. We managed to get people to question whether they wanted celebrity or they wanted competence. This time around I think that's the question … the contrast between him as a talk show host versus someone who can actually get in there — and maybe is not as glib or as charming — but can get the job done."

In 2008, Hollywood helped catapult Obama into the White House, as contributions and endorsements poured in from celebrities like Oprah Winfrey, Leonardo DiCaprio and Will Ferrell, and will.i.am of the Black Eyed Peas produced the viral, pro-Obama music video "Yes We Can" featuring famous faces like Scarlett Johansson and John Legend.

As Obama's term has progressed, though, some Hollywood liberals have expressed disappointment that he has not been more forceful on issues such as the environment and closing Guantanamo Bay. And one policy important to many in the entertainment industry — legislation to curtail online piracy — has so far failed to find support in the White House.

With the general election just gearing up, many in Hollywood are beginning to assess how involved they'll be in the race this time around.

Widely appealing stars like Clooney have value for a campaign beyond their deep pockets — they can be a potent tool for attracting interest among those who pay less attention to politics, according to USC professor Steven Ross, author of the book "Hollywood Left and Right: How Movie Stars Shaped American Politics."

"Clooney is not gonna alienate, like, say, Sean Penn would," said Ross, who compares the Oscar-winning star of films including "The Descendants" and "The Ides of March" to politically active actors of yesteryear like Gregory Peck and John Wayne. "His image is as a moderate, well-spoken, serious man who has done serious work."

Coming just a week after Obama officially kicked off his re-election campaign and as Mitt Romney has been all but crowned as the Republican nominee, the Clooney event is well-timed to take advantage of Southern California's traditional role as a cornerstone of Democratic campaign financing.